Locking circuit and control



March 13, 1951 R. E. scHocK LOCKING CIRCUIT AND CONTROL 3 Sheets-Sheet 1 Original Filed Nov. 23, 1945 March 13, 1951 R, E, SCHQCK 2,545,214

LOCKING CIRCUIT AND CONTROL Original Filed Nov. 23, 1945 5 Sheets-Sheet 2 INVENToR ROB RT E. SCHOCH. BY 7/`- t ATTORNEY IlI 5 Sheets-Sheet 5 R. E. SCHOCK LOCKING CIRCUIT AND CONTROL March 13, 1951 Original Filed Nov. 23, 1945 R O T N E V .N.

H C 0 H c s E T .K E R Patented Mar. 13, `1951 UNITED .STATES VENT ICE.

LOCKING CIRCUIT AND oorrrnoi.A

Robert E. Schock, Riverhead, N; Y., assignor toV Radio Corporation of America, a corporation of' Delawarev claimed a novel and simple direct current drive arrangement for the locking circuit in the form of'a cathode follower' stage, the cathode load impedance or a part thereof being included in the triggering circuit for the` locking stage.

f 'Ihe improvement disclosed in said application is ofE wide application in the signalling art and use" of myv invention is so intended. However; a particular use I nd forv the same is in control ,of gating tubes in diversity systems, such as, for example, diversity receivers for telegraphy, and` in particular for frequency shift signals.

In diversityy receiver systems of certain types the same signal is` pickeda up by antennas at spaced' points or of different propagation intercepting characteristics. The best signal is used and to. do so the same are compared to derive a; potential which isv used to select for use in the recording apparatus the said best signal. Inl my improved system, the derived potential is used, as described above to drive a locking circuit which opens the gate tube coupled to that receiver or antenna having the best signal. A further object of my invention is to provide improved' meansV for controlling a locking* circuit: by' the potential derived by the signal quality sensing means.

In this application which is a division of said aforementioned. abandoned application, I disclose improved means for deriving a control potential the absolute magnitude of which depends on which receiver of the diversity system is at' that instant getting the best signal and improved means for applying the sameto said control tube and improved means actuated by the locking circuit for selecting 'the best signal. In accordance with my invention the signal quality sensing means comprises two differential detectors which produce two direct current potentials of' a polarity whichindicates' which signal is best. A further object of my inventiony is provision 'of anfimproved diiierenti'al direct current drive arrangement for the locking circuit which responds positively to the derived potentials.

In frequency shift signaling systems the sig- 'nals are sent out by utilizing currents of' different frequency alternatively present, one repres'enting marking condition and the: otifierrepresenting spacingcondition. The currents. may

2^ Claims. (Cl. Z50- 205) be of high or low frequency, andpin the latter case they may be impressed on a carrier as modulation` and then recovered for recording Purposes at the receiver. The markingy and spacing currents are usually separated by several hundred cycles. My invention is in particular applicable tov signalling circuits as disclosed in Ui S. application Serial #632,978, led December 5`-, 1945, which has now ripenedl into Patent #2,515,668, dated July 18, 1950.

' In describing my invention in detail reference will be made to the attached drawings wherein Figs. 1 to 3 eachl illustrate a locking circuit and an improved control therefor arranged in accordance with my invention. In Fig. 1 the locking circuit is also included in a gating tube control arrangement as applied. to a diversity receiver system. The direct current loc-king circuit drive of Figs. 2 and 3 are similar, Fig. 2A being a simplilied version of the arrangement' of Fig. 3, which is added to expedite explanationI of my invention.

Referring now to Fig. 1, the triggering or locking circuit to be controlled comprises tubes or electrode' structures 2li and 25.. These electrode structures have their anodes and control grids cross-coupled by resistors 2l and 2|' and their a-nodes connectedv to a directl current source by resistors 23 and 23", and their cathodes connected to ground by resistor 25 to form a tripping circuit somewhat of= the nature disclosed in Finch U. S. Patent #1,844,950. Where faster tripping action is necessary a double locking circuit is used and may then be as illustrated in Fig- 1. The double locking circuit includes additional tubes 26 and Zaswith their anodes and control grids cross-coupled by resistors 21 and 2'1, as shown, to form a secondV locking circuit. The control grid of tube 2S is coupled to the anode of tube 2i) by a capacitor 4l), while the control grid of the tube 28 is coupled to the anode of the tube 2d. by a capacitor 40. The arrangement is such that when current is caused to flow in say tube 2c, thepotenti'al at the anode of' this tube drops" slowly for aportion` of the tripping cycle. The potential at the control grid of' tube 2tlikewise falls slowly soV that' current through the tube 2t' is reduced' slowly for a part of the locking or tripping action. At the end oi' the tripping action the current through 20- growsrapidly to saturationr so that the potential on the anode end: of capacitor 40 falls sharply and this applies. a quickly falling potenti'al to the control grid of` tube 25'; At' the same Vtime a sharply rising; potential. is applied cuit is triggered to one condition of stability it f remains there until the potential on the grid of tube changes in a direction to trigger the locking circuit to the other condition of stability. 'Ihedouble locking tube circuit is as disclosed in U. S. application Serial #632,978, iiled 5' December 5, 1945, Patent #2,515,668, as are the gating tubes 86 and 66, their use and their coupling by resistances 84 and 84 over grid bias clamping tubes 9D and 90 etc. to the locking circuit. 'I'hey are also described to the extent 'necessary hereinafter.

The triggering of the locking circuit is to be controlled in accordance with a direct current potential of varying magnitude such as might appear across resistor 56. Assume, for example, that the potential at the upper Vend of resistor 56, say at Y, is about zero, or slightly positive, and that potential at the lower end of resistor 56 varies from a value substantially equal to the potential at Y to a positive or negative value.

The end Y of the resistor 56 is connected by resistor 56 to the cathode of a direct current trigger driver or control tube 66. The control grid 64 of this tube is yconnected to the other end of resistor 56. varies up and down with respect to zero potential and the triggering action is to be controlled in accordance with this potential. The tube 60 is a cathode follower stage and its cathode is connected by resistor 56 and resistor 66 to ground. The-resistor 66 is also in the direct current bias circuit for the control grid |58 of the locking circuit tube 2B. When the potential at the point -A becomes less negative, more current ilows in the tube 6D, whereas when the potential at the point A becomes more negative, less current iiows in the tube 60. The potential drop on the grid 68 depends upon the current owing in resistors 56 and 66, l. e., in the tube 6|) and this potential at grid 68 is positive at all times. However, the cathodes of tubes and 2d are also positive by the amount of potential drop across resistor 25. The grid 68 potential is as a consequence slightly negative with respect to the cathode potential. Tube 6B is self-biased to the middle of its operating range so that when the potential across resistor 55 is zero tube 60 is in the middle of its operating range. When A swings negative with respect to Y tube 6B draws less current through resistors 56 and 66 so that the potential at the grid 68 becomes more negative and current is cut off in tubes 20 and28 and flows in tubes -24 and 26. When the potential at A swings less negative the current flow in resistors 56 and 66 increases to provide at the control grid 68 a less negative potential so that current iiows in the tubes 20 and 28, and is cut off in tubes 24 and 26. The potentials at the anodes and grids of tubes 26 and,28 and at various points in the circuit of this stage vary differentially through a range which is large as compared to the variation of the potential at point A. These differential potentials appear across resistors 85 and 85 for use as desired. They` vary between a small posi- The potential at the point A -LlO 4 tive Value and a relatively large negative value. In the example illustrated, they are used to control the conductivity of the pair of gate tubes and 66. The control grids of tubes 26 and 28 are connected to the control grids of tubes 8B and 86' by resistors 82y and 84, and 82 and 84'. Thus the potentials on the control grids 86 and 86 are varied differentially with respect to the cathcdes of tubes 80 and 8B'. The resistors 82 and 82 serve as described in U. S. application Serial #618,760, filed September 26, 1945, now Patent #2,511,093, dated June 13, 1950, to provide on the control grids 86 and 86' potentials which vary differentially through a wide range in accordance with variations in the potential at A and/or atgrid 68.

The potentialdeveloped across resistor 5U may be of a magnitude which varies in a direction to indicate which of two receivers has the best signal. The arrangement may then be as described in said U. S. application Serial #632,978, led December 5, 1945, Patent #2,515,668. A pair of diiTerential diodes IUI] and |00 are respectively coupled by tuned intermediate frequency transformers T and T to the IF output of a receiver (not shown) designated #3, and IF outputvof the same frequency from a receiver (not shown) designated #2. The transformers T and T' (which may operate at 50 kc.- the fref quency shift FS) are broadly tuned so that they Will pass, without substantial frequency selection or attenuation of any part of the frequency spectrum, a band of frequencies sufficiently wide to include the mark and space frequenciesl transmitted by the frequency shift transmitting system. The transformer T and rectifier |60 and transformer T and rectifier |08 form a differ,-5 ential detector system by means of which poten'- tials are developed across the cathode circuits |64 and |64 in opposed polarity. The networks |64 andy IM' filter out the alternating current components of intermediate frequency and leave the direct current componentsv which are of amplitudes depending on signal strength. When the receiver connected with transformer T gets the best signal the potential drop across the unit |04 is greater than the potential drop across the unit |04. Since the cathodes lof both diodes |66 and |00 are relatively positive the'potential at the point A will be more negative when the current ow in diode |66 is largest and less negative when the current ow in diode |06' is greatest. Thus the potential at the point A varies in a direction, positive or negative relative to the potential at Y, depending upon which signal is strongest. The time constants of networks |04 and |04 are'large so that the direct current potentials vary slowly in accordance with signal strength but do not follow faster variations ofv say audio frequency.

The tubes 80 and 80 may be gating devices in a diversity receiver, in which case the output of receiver #3 may be also coupled to a grid in the device 80 by an IF amplifier |20, a current amplitude limiter |22, and a frequency discriminator and amplitude modulation detector |24, and condenser |26. The-#2 receiver maybe similarly connected to a grid in the gating device 8D' by an amplier |20', alimiter |22', adifs criminator |24', and a coupling condenser |262 The arrangement is again as illustrated in said U. S. application Serial #632,978, led December 5, 1945, Patent #2,515,668. f l

In somecases alarger direct'current driving potentialis: desired on thecontrol grid 64., 'I h en the connection between this control grid and the point A may be broken say at X and the grid Gc is then connected to the point B by say a switch or by permanent connection. Then the total op across the units 94 and ital may be ed. Resistors 56 and i' may then be removed by breaking the circuits at points Y and Y.

Where a balanced direct current driving circuit for the locking tubes is desired, an arrangement as illustrated in Fig. 2 may be used. In the circuit of Fig. 2 a cathode follower' drive stage including tube 92 and tube 99 is supplied for each side of the locking circuit. The tube dii is ccnnected as in Fig. l. The tube te is similarly connected to the control grid G9 of tube 2li. Resistors 56 and 5t are of about like value and resistors 66 and 5S' are of about like value. This embodiment by being so arranged provides a confipletely balanced locking circuit with a substantially completely balanced differential direct current drive tube arrangement therefor. The tubes 6Fl andl 'are of the cathode follower type and have the points between their cathode resistors 56 and 96 and 56' and ti connected to the control grids 68 and ES' respectively oi tubes 29 and 24. This includes the resistors '55 and 5E in the grid bias circuits for tubes Ei@ and G9 respectively. The potentials on the control grids @fl and 6d of the cathode follower stages are varied differentially. To simplify the arrangement l have shown the same as being supp-lied by dii- Cil ferentially operated potentiometers 5i and til. Y

However, it must be noted that the potential source BC has its polarity reversed with respect to the potential source BC so that when the potential on the control grid dll becomes more negative the potential on the control grid 84 becomes less negative and vice versa.

In Fig. 3, I have illustrated a circuit arrangement for deriving differentially varying direct current potentials for control of the tubes t@ and 60' of an arrangement as in Fig. 2. Moreover, in this Fig. 3 the differential potentials vary in a i direction to denote which of two Vreceiver signals is the best. The locking circuit as controlled drives a second or cascaded locking stage as in Fig. 1. The double locking stage controls a pair of gating tubes also as in Fig. l. The arrangement of Fig. 3 is as in Fig. l and Fig. 2, except as otherwise noted hereinafter. The transformers T, TI, T and Tl are tuned as described in connection with transformers T and T in Fig. 1. Transformers T and Ti each have a primary winding coupled to one receiver and a secondary winding coupled to one diode of two pairs of diodes |00, |00 and Il and lili. Transformers T and T l are similarly coupled by their primary has the best signal. The transformers Ti and TI are similarly coupled to the differential detectors IUI and IDI with their load units H15 and 05. It will be noted that in Fig. 1 the differentially connected diode rectier loads are between the cathodes of the rectifler's, whereas in Fig. 3 these loads are between the anodes of the diode rectiliers. The potentials at the anode ends oi the load units |94 and iGLi are negative and the potentials oppose. It will be seen then that when the receiver #t has the strongest signal the grid lili oi tube iid will become more negative or less positive, and when the .ft2 receiver has the strongest signal the grid St of tube 59 will become more positive or less negative. On the contrary, when the #2 receiver has the best signal the grid of tube Sil will become less negative or more positive, and when the #2 receiver has the best signal the grid Ed of tube 99 will become more negative or less positive. This provides the differential control action necessary to operate the balanced trigger circuit as stated in connection with Fig. 2. The gating tubes are controlled as described in connection with Fig. 1 to let pass the signal from the #t receiver or from the #2 receiver, depending upon which receiver has the best signal as determined by the pair of differential rectiers supplying the direct current driving potential for the locking circuit control tubes.

What is claimed is:

1. In a diversity system, two radio receiver devices responsive to signal energy, a gating devicer coupled to each receiver, said gating devices having electrodes, a common output circuit coupled to output electrodes of the gating devices, a locking circuit including two electrode structures having two conditions of stability in which one structure is conductive and the other non-conductive and vice versa, couplings between points on the locking circuit at which dierentially varying potentials appear and corresponding electrodes in the two gating devices, two differential rectifier systems each coupled to both receivers for providing two control potentials one for each structure of the locking circuit, and a locking circuit driver tube, one for each provided control potential, coupling each differential rectier system to a different structure of the locking circuit.

2. In a diversity system, two radio receiver devices responsive to signal energy, a gating device coupled to each receiver, a common output circuit coupled to the gating devices, a locking circuit including two electrode structures having their input and output electrodes cross-coupled to provide only two conditions of electrical stability in each of which a corresponding one of the structures is conductive and the other nonconductive, a differential coupling between the locking circuit and the two gating devices, two differential rectifier systems each coupled to both receivers for providing two control potentials one foreach structure of the locking circuit, and separate means, one for each provided control potential, coupling each differential rectier system separately to a different structure of the locking circuit.

ROBERT E. SCI-IOCK.

REFERENCES CITED The following references are of record in the le of this patent;

UNITED STATES PATENTS Number Name Date 2,269,594 Mathes Jan. 13, 1942 2,414,111 Lyons Jan. 14, 1947 2,478,977 Nicholson Aug. 16, 1949 

